Positively charged ions gain electrons at the cathode. These are half equations for some reactions at the cathode:
Na+ + e- → Na
Pb2+ + 2e- → Pb
2H+ + 2e- → H2
Balance the half equation for the formation of aluminium during electrolysis: Al3+ + e- → Al.
The balanced half equation is: Al3+ + 3e- → Al (because three negatively charged electrons are needed to balance the three positive charges on the aluminium ion).
Write a balanced half equation for the formation of calcium from a calcium ion, Ca2+.
Ca2+ + 2e- → Ca
Negatively charged ions lose electrons at the anode. For example
2Cl- → Cl2 + 2e-
2O2- → O2 + 4e-
Write a balanced half equation for the formation of oxygen from hydroxide ions.
4OH- → 2H2O + O2 + 4e-
Write a balanced half equation for the formation of bromine, Br2, from bromide ions, Br-.
2Br- → Br2 + 2e-
This means that:
This can be seen by looking at the half equations above.
It helps to remember OIL RIG - Oxidation Is Loss of electrons, Reduction Is Gain of electrons.